1. Field of the Invention
This invention relates to wireless wide area networks and, more particularly, to handling dormancy timers in a CDMA 2000 wireless network.
2. Discussion of Related Art
Subscribers are adopting wireless communications in increasingly large numbers. This trend is being fueled further by the attraction of wireless data. It is widely surmised that access to data services for mobile users will experience the magnitude of explosive growth witnessed in wire-line networks. New higher data rate interfaces under proposal are promising increased levels of bandwidth and access, rivaling that of wire-line networks.
So-called third generation (3G) networks are being proposed to provide higher data rates and other improvements. FIG. 1 illustrates an exemplary architecture of a 3G network in accordance with the CDMA 2000 proposal.
In the exemplary network, mobile stations 102 communicate over an air interface 103 with a radio access network (RAN) 104. The RAN 104 includes Base Transceiver Stations (BTS) 106 that are in radio contact with the mobile stations and that are in fixed line communication with a Base Station Controller (BSC) 108. The BSC 108 controls the radio equipment used to communicate with the mobile stations. This function is collectively referred to as Radio Resource Management, and it encompasses the management of handoffs of the roaming mobile stations 102 within a BSC and the allocation of radio channels for both voice and data traffic.
The BSC communicates with a Mobile Switching Center (MSC) 112, which is a standard Local End Office with enhanced call processing software (including mobility management) and (optional) hardware that can perform transcoding and rate adaptation functions. The traffic carrying capacity of the MSC is engineered using standard Erlang Traffic Management techniques. Traffic is assumed to adhere to Poisson arrivals with exponentially distributed holding times of the order of hundreds of seconds. Typically, signaling information between the RAN and the MSC is conveyed in accordance with a predefined protocol, and voice data is conveyed over bearer circuits in accordance with other protocols. Among other things, the MSC 112 provides mobility management functionality. This function consists of management of mobile station parameters such as the location of a mobile station, mobile identity and authentication. Handoffs between BSCs and between MSCs are controlled by the MSC. The MSC communicates with the Public Switched Telephone Network (PSTN) 114 using known signaling and bearer circuit protocols. A salient feature of these architectures is an end-to-end circuit telephony paradigm in which the explicit reservation of resources ensures service quality.
The 3G networks include new functions, not found in earlier proposals, to support packet data access networks (as opposed to circuit networks). For example, the CDMA2000 proposal includes two new network functions: the Packet Control Function (PCF) 110 and the Packet Data Serving Node (PDSN) 116. The PCF 110 may be co-located with the BSC 108 within the RAN 104. The PDSN 116 may be independently located and may communicate with the PCF via a Radio to Packet (R-P) interface. The PDSN communicates with an IP network 118 using IP based protocols.
The PCF 110 is responsible for ensuring that the packet data services are delivered properly on the radio side; i.e., over the air interface to the mobile stations 102. The PCF interfaces directly with the PDSN 116 to transfer user packet data through an interface called the R-P (Radio to Packet) interface. The PDSN 116 is a gateway to the data network 118 and terminates a logical link layer (PPP) to the mobile station 102. In short, it acts like a router for the data between the application on the mobile station 102 and the packet data network 118.
A key component of the CDMA2000 proposal is that call processing and mobility management remain under the purview of the MSC 112. The MSC sets up and releases all packet-switched data calls. It also manages the handoffs. Thus the MSC retains its key positioning in a CDMA2000 packet data network by continuing to provide a core set of functions.
The most valuable resource in a wireless network is the frequency spectrum allocated to the network operator. Maximizing the use of this resource, i.e., supporting as large a number of subscribers xe2x80x9con the airxe2x80x9d as possible, is a crucial advantage. Circuit telephony, with its paradigm of explicit reservation of resources, does not make effective use of the spectrum resource if it dedicates unused resources to subscribers. This is widely recognized and the traditional solution is the so-called xe2x80x9cbusy hourxe2x80x9d assumption, viz., that not all the subscribers to a resource will simultaneously attempt to use the resource and, moreover, the time a subscriber utilizes the resource, i.e., the holding time, will be limited. Under this assumption the number of subscribers that can be supported may be larger than the number of radio channels available in a RAN. This increase in subscribers is also referred to as the gain due to the statistical multiplexing of call arrivals.
The magnitude of statistical multiplexing gain relative to a given subscriber population is dependent on the holding time and the rate of call arrivals (number of calls in a given time period). In traditional mobile telephony the holding time of calls is assumed to be exponentially distributed with a mean value of 2-3 minutes. The rate of call arrivals has been extensively studied and a number of different statistical distributions have been proposed to capture the rate of call arrivals. The architecture of traditional circuit switches has most often been influenced by assuming that the rate of call arrivals is a random variable whose probability density function obeys the Poisson formulae. The key point in assuming that call arrival is a Poisson random variable implies that the mean and variance of this variable are the same; thus, the mean rate and variance of call arrivals at a switch does not significantly differ for a given set of subscribers. Intuitively, subscribers are not expected to make all of their calls in a very short period of time, or that the interval between successive calls does not vary by a large factor, i.e., the inter-call arrival time obeys an exponential distribution. Historical traffic analysis has borne out the viability of these assumptions. The behavior of a large set of subscribers in the aggregate over a large time interval exhibits Poisson characteristics.
The impact of packet switched data on spectral efficiency is of paramount importance. The mobile station is expected to operate in an xe2x80x9calways onxe2x80x9d mode in which a data session is established when the mobile station is powered on and this session is maintained until the mobile station is powered off. It would be infeasible to follow the circuit telephony paradigm and allow packet switched data calls to hold resources until the session is terminated.
To make more effective use of resources, a proposal called xe2x80x9cdormancyxe2x80x9d has been made to explicitly request and reserve spectral resources during a packet data session. Air resources should be released during the dormancy period so that other packet switched data sessions can make use of the spectrum; i.e., more subscribers can be supported on the same number of radio channels. An integral component of the dormancy proposal is that the PDSN is unaware of any issues related to dormancy. The function of granting and releasing air resources is delegated to either the BSC/PCF complex 108, 110 or the MSC 112.
The dormancy specification envisages a xe2x80x9cdormancy timerxe2x80x9d maintained by the BSC 108 for every packet data session. This timer is started by the BSC and mobile station after every packet reception or transmission. If the timer expires before the next packet reception or transmission, the air resources for that session are released. The request and release messages due to expiration of the dormancy timer for every packet data session appear as new call requests and releases to the MSC 112.
Proposals for managing and handling the dormancy timers have been lacking or are believed to be inefficient.
The invention provides methods and systems for determining and maintaining dormancy timers for subscribers in a wireless wide area network that promote efficient use of the radio channels.
Under one aspect of the invention, subscriber usage is monitored to determine subscriber usage statistics. Based on the subscriber statistics, a dormancy timer value is determined for a given subscriber. The dormancy timer for the given subscriber is then set with the dormancy timer value.
Under another aspect of the invention, the subscriber usage statistics are for a given user. In yet another aspect of the invention, the subscriber usage statistics are for a class of subscriber.
Under still another aspect of the invention, histogams are used to approximate the probability density function of a user""s silent time periods. The histogram is used to maximize a gain equation that is a ratio of the probability of a user being silent longer than d+{overscore (T)}+3 "sgr" versus the probability of a user being silent longer than d, where d is the dormancy interval, {overscore (T)} is the mean and "sgr" is the standard deviation of the talk time distribution.